clippy::complexity fixes

filter_map_identity
 needless_bool
 search_is_some
 unit_arg
 map_identity
 needless_question_mark
 derivable_impls

compiler/rustc_smir/src/rustc_smir/context.rs

@@ -157,7 +157,7 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
                 (name == crate_name).then(|| smir_crate(tables.tcx, *crate_num))
             })
             .into_iter()
-            .filter_map(|c| c)
+            .flatten()
             .collect();
         crates
     }